Typically, a coaxial loudspeaker system consists of a high frequency transducer and one or more lower frequency transducers. The high frequency transducer can be mounted in front of or even within a lower frequency transducer.
Coaxial loudspeaker transducers make it possible to build 2 or 3 way loudspeaker system with smaller frontal area than conventional side by side transducers. The coaxial loudspeaker transducers also have an advantage of sound radiating from acoustically a single source for more even directivity pattern.
Disadvantage of the typical coaxial loudspeaker system is diffraction around the edges of the high frequency transducer housing. Diffraction of sound waves occurs when a sound wave encounter an obstacle that is comparable in size to the length of the sound wave. In a coaxial loudspeaker system, when a sound wave radiated from the diaphragm of a lower frequency transducer reaches the edge of high frequency transducer housing and is reflected by the edge of high frequency transducer housing, if the wavelength of the sound wave is comparable to the edge of the high frequency transducer housing, the reflected sound wave interferes with a subsequent sound wave with a similar wavelength propagating from the diaphragm of the lower frequency transducer. This interference between sound waves causes diffraction. The diffraction in turn causes irregular frequency response.